Electrically operated motor vehicles or electric vehicles have an electrically chargeable energy store. The latter may be configured as a high-voltage battery, the rated voltage of which may be 800 volts, for example. Such an energy store is typically charged by establishing an electrical connection between an external charging column (charging station) and a charging socket fitted to the vehicle. A switchable electrical connection is provided between the charging socket and the vehicle battery, specifically by means of the switch arrangement, which may also be referred to as a disconnector and may be embodied as a contactor, for example. The switch arrangement is initially open at the beginning of a charging process, in order to bring the voltages of the vehicle battery and of the charging socket to almost the same value. Afterward, the switch arrangement is closed and the vehicle battery is charged.
In order to measure the first and second electrical variables, for example in the form of a voltage measurement, a high measurement accuracy is required. This is because the voltage difference is permitted to be only very small for technical reasons, for legal reasons and for reasons relevant to safety.
In this case, the accuracy of the voltage measurements is also not permitted to decrease over the entire operational time of the components.
DE 10 2013 221 970 A1, which is incorporated by reference herein, describes a charging system for a plug-in vehicle which can be connected to a charging column via a windable charging cable and can be charged. In this case, the current and the voltage are measured during a charging process and the resistance of the charging cable is thus calculated.
DE 10 2014 208 696 A1, which is incorporated by reference herein, discloses a charging apparatus for an electrically operated vehicle, wherein the charging apparatus has an interface with a contact part, a power converter, a control unit and a circuit-breaker and is configured to detect a voltage between the contact part and the circuit-breaker.
Furthermore, US 2009/0128158 A1, which is incorporated by reference herein, discloses providing an apparatus for the voltage measurement of a plurality of battery modules interconnected in series. A difference voltage is determined during the discharging process of two capacitors in the charged state and in the uncharged state. A measurement error is calculated therefrom.
US 2012/0313562 A1, which is incorporated by reference herein, discloses a battery control unit for an electric vehicle that can determine the present voltage of each individual battery cell during a charging process and adapt the charging voltage.
Finally, WO 2012/139778 A2, which is incorporated by reference herein, discloses a method for charging an electric vehicle, wherein the charging current is adapted to the temperature of the electrical connection between the charging apparatus and the vehicle in order to prevent the electrical connection from overheating.